On the nutrition facts label, we always look at the total number of carbs to calculate what Lainey's eating and how much insulin she'll need.
Here's a model on how to "count carbs". I can't imagine not having the nutrition facts label as a reference. I spoke to someone who's children were diagnosed with diabetes in the '70's and '80's when it wasn't mandatory to have this label on food packages. We would be lost without it! Most serving sizes are 1/2, 3/4, or 1 cup, but when you're feeding a 14 month old you're not going to give her a full up of cereal. I remember calling Dustin at work one day because I couldn't figure out the carbs to serving ratio. I was almost in tears I was so frustrated, but he eventually told me how many carbs were in a 1/8 cup of a 3/4 cup serving size.
A couple months ago my parents watched my girls for me. My dad asked to borrow the carb counting book for a reference. I told him I didn't bring it. "How do you know the carbs of certain foods then," he asked. "It's all up here," I said, pointing to my head.
I can't tell you how many servings sizes to carb ratios I have memorized.